Researchers from Brown University claim that they have figured out the reason why a person feels lethargic after the first night of sleep in a hotel room or any other place that is not his or her home. It is because half of our brain stays awake when we sleep in unfamiliar territory. Researchers drew the conclusion after monitoring the brain activity of a small group of people during their sleep in a lab.

For the study, researchers enrolled 11 participants and asked them to sleep in a laboratory where their brain activity, eye movement and heart rate were constantly monitored through various scanners.

Researchers found that on the first night of the experiment one of the two hemispheres of the brain remained alert. Therefore people struggled to sleep well on the first night in a new place and also it took longer to fall asleep.

Researchers noticed that the slow wave activity which is associated with deep sleep was significantly lighter in the left side of the participant’s brain. The issue what they call “first-night effect” was gone by the second night.

To test whether left side of the brain stayed awake in the new place, researchers conducted another experiment. This time around, participants slept in a normal bed but with wearing a pair of headphones. Then, researchers produced sound of beeps by each ear of the sleeper either steadily or frequently.

Researchers found that left side of the brain reacted more strongly to those sounds compared to right side but only on the first night. Moreover, more participants woke up when beeps were played on the left side of their brain. The brain patterns observed during the first night of sleep were not observed in the subsequent nights.

“We know that marine animals and some birds show unihemipheric sleep, one awake and the other asleep. The new findings suggest “that our brains may have a miniature of what whales and dolphins have.” Lead researcher Yuka Sasaki from Brown University said.

Researchers believe that the effects of sleeping in a new place may be reduced if people take their own pillows and sheets with them or stay in those hotels or places that appear similar to their home or bedroom.

Masako Tamaki co-author of the study says. “Well, you might be able to reduced first-night effect, but we are not really sure if you can remove the effect completely.”